Скачать или смотреть Cover crop management to reduce nitrogen leaching loss from cropland

Presentation to the 2022 World Congress of Soil Science in Glasgow, Scotland. by Ray Weil, Fang Wang, Sarah Hirsh, and Nathan Sedghi.
Nitrogen from cropland is a major water pollutant and a major driver of eutrophication in lakes and estuaries. Cover cropping is a tool for controlling the leaching loss of soluble nitrogen during the winter months in temperate regions. However, cover crop management is rarely optimized to reduce nitrogen leaching. Our research in Eastern USA over 10 years shows that aboveground cover crop nitrogen exceeds soil nitrogen reductions in 0-1 meter and that large pools of soluble nitrogen remain after cash crop harvest with much of this deeper than 90 cm in the soil and very susceptible to winter leaching. We show that the time of cover crop establishment is critical to their being effective during the fall-winter-early spring leaching season. Our new model of cover crop nitrogen leaching reduction suggests the critical cover crop action is the early fall removal of soluble nitrogen from the deep soil profile, so when drainage water passes through the profile during winter and spring because of high rainfall and low ET it encounters little soluble nitrogen to dissolve and carry away. A few weeks planting time difference in late summer can dramatically affect nitrate concentrations in drainage water from December through May. Inter-seeding into standing cash crops is one technique for getting cover crops planted early with significantly more growing degree days to develop root systems that capture deep nitrogen. Late-planted cover crops accomplished little more leaching reduction than winter weeds. Governments should incentivize early cover crop planting.